/* =============================================================
 * Your Grandmother's guide to Algorithms
 * =============================================================
 *
 * Copyright (c) 2007, Saverio Miroddi
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 *     * Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright 
 *       notice, this list of conditions and the following disclaimer in the 
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the SaverioMiroddiSoftware nor the names of its 
 *       contributors may be used to endorse or promote products derived from 
 *       this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER 
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *  
 * ---------------------------
 * BitInputStream.java
 * ---------------------------
 *
 */
package huffman;

import java.io.ByteArrayInputStream;

/**
 * Read a byte array as a stream of bits.
 *  
 * @author Saverio Miroddi
 */
public class BitInputStream
{
	private static final int BITS_PER_BYTE = 8;

	private final ByteArrayInputStream _input;
	
	private boolean[] _currByte;
	
	/** points to next bit */
	private int _bitPtr;	
	
	public BitInputStream(byte[] input)
	{
		_input = new ByteArrayInputStream(input);
		_currByte = new boolean[BITS_PER_BYTE];
		
		// force read at first readNextBit()
		_bitPtr = _currByte.length; 
	}
	
	/**
	 * Watch out! Doesn't return a signal of stop, so the client class must know
	 * exactly when to stop.
	 */
	public boolean readNextBit()
	{
		if (_bitPtr == _currByte.length) {
			_bitPtr = 0;
			int byteRead = _input.read();
			
			if (byteRead == -1) return false;
			else _currByte = decodeByte(byteRead); 
		}

		return _currByte[_bitPtr++]; // ++
	}

	public static boolean[] decodeByte(int byteRead)
	{
		boolean[] bits = new boolean[BITS_PER_BYTE];
		
		for (int i = 0; i < BITS_PER_BYTE; i++) {
			int bit = byteRead & (1 << (BITS_PER_BYTE - 1 - i));
			bits[i] = (bit > 0) ? (true) : (false);
		}
		
		return bits;
	}	
}